In hopes of producing oil and gas more efficiently, the petroleum industry continuously strives to improve its recovery systems. As such, those in the industry often drill horizontal, deviated, or multilateral wells, in which several wells are drilled from a main borehole. In such wells, the wellbore may pass through numerous hydrocarbon-bearing zones or may pass for an extended distance through one hydrocarbon-bearing zone. Perforating or “fracturing” the well in a number of different locations within these zones often improves production by increasing the flow of hydrocarbons into the well.
In wells with multiple perforations, however, managing the reservoir becomes difficult. For example, in a well having multiple hydrocarbon-bearing zones of differing pressures, zones of high pressure may force hydrocarbons into zones of lower pressure rather than to the surface. Thus, independent control of hydrocarbon flow from each perforation, or zone of perforations, is important to efficient production.
To independently control hydrocarbon flow from each perforation, or zone of perforations, those of skill in the art have inserted production packers into the well annulus to isolate each perforation. Valves disposed on the production tubing control flow into the tubing from each perforated zone. One type of valve used in the industry for this function is the sliding sleeve valve. Typical sliding sleeve valves are disclosed in U.S. Pat. Nos. 4,560,005, 4,848,457, 5,211,241, 5,263,683, and 6,044,908, which are incorporated by reference herein in their entireties. In such a valve, a sleeve capable of longitudinal movement with respect to the production tube is located between a sleeve housing and the production tube. One or more ports extend radially through the sleeve, the housing, and the production tube. When the sleeve is in an open position, the ports of the sleeve, housing, and production tube are aligned such that fluid may flow through the ports and into the production tube. When the sleeve is in a closed position, the ports of the sleeve are not aligned with the ports on the housing or production tube, preventing fluid flow into the production tube. Although the sleeve can be moved longitudinally between the open and closed positions by several different means, it is common for such control to be hydraulic, essentially pushing the sleeve in a piston-like manner. (Valve control, however, can also be motor-driven or manually actuated).
In addition to this valve being utilizable fully open or fully closed, systems have been developed that allow for incremental valve positioning. For example, U.S. Pat. Nos. 5,211,241 and 5,263,683, incorporated by reference herein in their entireties, disclose sliding sleeve valves capable of such incremental positioning. The ability to incrementally position valves in different hydrocarbon bearing zones allows for greater control of overall fluid production by permitting the creation of pressure drops across certain production zones. Knowledge of the exact position of the valve is thus necessary to create optimal pressure drops, and thus to maximize production. However, over time, the exact incremental position of the valve becomes difficult to determine due to corrosion, scaling, seal wear, in-well contaminants, mechanical damage, hydraulic leaks or electronic component failures. Thus, the user might believe he is controlling the sleeve to a certain position, when in reality the valve is not properly positioned and therefore is allowing more or less ingress into the production tube than the user intended.
In another prior art technique, the amount of ingress into the production tube through the sliding sleeve valve is controlled by “duty cycling” the valve between a fully open and fully closed position. In this scheme, if it were desirable to allow a 20% ingress, the sleeve would be fully opened for a time period, e.g., 1 second (or minutes or hours), and then would be fully closed for 4 seconds (or minutes or hours), and this procedure would be repeated over and over. This repetitive scheme constitute a 20% duty cycle and thus approximates the ingress into the production tube that would be allowed if the sleeve were left at a 20% open position. However, cycling the sleeve between fully opened and fully closed positions is not desirable, as this causes the sleeve to exhibit excessive wear and strain, and eventually failure.
Rotational sleeve valves are also known in the art. In a rotation sleeve valve, the sleeve component is not linearly shifted within its housing, but instead is rotated within its housing to open or close the valve. An example of a rotary sleeve valve comprises a hydraulic control actuating unit, which as known is used to route controlling hydraulics to different down hole components by rotating the valve. For example, when the sleeve is at its 0 degree orientation, it may communicate hydraulic fluid from the surface to a first down hole component; when rotated 90 degrees, it may communicate hydraulic fluid to a second down hole component, and so on for the 180 and 270 degree orientations. (Angular spacings other than 90 degrees may also be used). As with longitudinally sliding valves such as the sliding sleeve valves disclosed above, it is also useful to be able to verify the rotational position of such rotating sleeve valves.